1. Bake the Cake Layers

• Preheat your oven to 350°F (175°C). Grease and line two 8-inch cake pans with parchment.
• In a medium bowl, whisk together the flour, both cocoas, baking powder, baking soda, and salt.
• Set aside. In a large bowl, cream the butter and sugar together until light and fluffy (about 3–5 minutes).
• Beat in the eggs one at a time, then stir in the vanilla. In a small bowl, combine the blackberry puree, buttermilk, and oil.
• Alternate adding the dry ingredients and wet mixture into the creamed butter, mixing gently until just combined.
• Divide the batter evenly between your pans. Bake for 25–30 minutes or until a toothpick comes out clean. Let cool completely before assembling.

2. Make the Blackberry Filling

• In a saucepan over medium heat, cook the blackberries, sugar, lemon juice, and cinnamon stick for 5–7 minutes.
• In a small bowl, stir the cornstarch and water together. Add this to the berries and cook until thickened. Remove from heat and cool. You can strain out the seeds if preferred.

3. Prepare the Ganache

• Heat the cream in a small saucepan until just simmering. Pour it over the chopped chocolate in a heatproof bowl.
• Let it sit for 2–3 minutes, then stir until smooth. Add butter for extra shine if you’d like. Let cool until thickened but still pourable.

4. Assemble the Cake

• Level the cake layers if needed. Place one layer on a cake stand or serving plate. Spread a thin layer of ganache over the cake, then spoon on the blackberry filling.
• Top with the second cake layer. Pour the ganache over the top, letting it drip down the sides naturally.

5. Decorate and Serve

Finish with fresh blackberries, edible flowers, or spooky decorations like chocolate skulls. Let the ganache set for 20–30 minutes before slicing.